A spider that only eats ants is choosy about which body parts of its prey it devours based on their nutritional value. These new findings are the first to demonstrate that "specialist" predators relying on a single food source might have evolved feeding behaviors to maximize what they get out of meal time, the researchers say.

"We found that these spiders do have to balance their nutrient intake by choosing different body parts of their exclusive ant prey," said Stano Pekár, an assistant professor of ecology and zoology at Masaryk University in the Czech Republic and lead author of the research published in the April 15 issue of the journal Animal Behaviour.

When chowing down on ants, the spiders consistently began with the protein-packed front parts before getting to the fattier hind segment, called a gaster or abdomen. The picky eating seemed to pay off: Spiders reared on just front-end ant pieces grew faster, bigger and lived longer than those served only gasters or even whole ants.

Yet when given the option, spiders still gobbled on the gaster rather than shunning it entirely for the front parts, hinting that the gaster contains vital nutrients not found elsewhere in the ant's body.

Feasting on ants - For the experiments, the researchers collected dozens of Zodarion rubidum, an ant-eating spider species found in Europe and the United States that has a light orange head and legs.